System For Welding Motor Vehicle Bodies

ABSTRACT

In a welding system comprising a welding station and various pairs of side frames, which can be positioned selectively in the welding station for clamping in the welding position bodies of different types, are provided magazines of side frames both upstream and downstream of the welding station. There are moreover provided auxiliary guide means, which connect directly together at least one magazine upstream of the welding station and at least one magazine downstream of the welding station so as to enable transfer of pairs of side frames directly from a magazine upstream to a magazine downstream or vice versa, without passing through the welding station.

BACKGROUND OF THE INVENTION

The present invention relates to systems for welding structuresconstituted by stamped sheet-metal elements, such as motor-vehiclebodies or their sub-assemblies, said systems being designed to operateon a plurality of different types of structure to be welded (forexample, bodies of various models of motor vehicle, or bodies ofdifferent versions, such as saloons, station wagons, cabriolets, etc.,of the same model of motor vehicle, or again, for example, individualsub-assemblies, such as the floor panel or sides, of various models ofmotor-vehicle body). There are known systems of the type specified above(see, for example, GB-A-2 172 555 and EP-A-0 642 878, filed in the nameof the present applicant), which comprise:

a welding station;

a conveying line, for carrying through the welding station thestructures to be welded or at least part thereof; and

a plurality of pairs of side frames, which are provided with means forclamping the structures to be welded during welding and can be guidedalong the conveying line, the clamping means provided on the side framesof each pair being adapted to the configuration of a corresponding typeof structure to be welded.

In the above known systems, the side frames are movable on guide meansprovided at the side of the conveying line, to enable replacement,according to the type of structure to be welded, of the pair of sideframes that is located near the welding station. Each side frame isdisplaceable between one first position, close to the welding station,and at least one second position, remote with respect to the weldingstation.

In addition, when each pair of side frames is in the aforesaid firstposition close to the welding station, it is displaceable between anopen condition and a closed condition, in the latter of which therespective means of clamping of the side frames are operative forclamping parts of the structure to be welded in a welding configurationin the welding station. The system moreover comprises means for movingthe side frames, for their displacement between the respective first andsecond positions.

In order to facilitate use of various types of side frames, it islikewise known to equip the system with one or more magazines of sideframes, each comprising one or more parking stations both upstream anddownstream of the welding station, with reference to the direction ofadvance along the line, each station comprising a guide section designedto support a side frame in a slidable way.

Thanks to the pre-arrangement of the magazines of side frames, it ispossible for a station to operate in a flexible way on a large number ofvarious types of structure to be welded.

SUMMARY OF THE INVENTION

The purpose of the present invention is to improve further the knownsystems by further increasing their degree of flexibility and theproductivity of the line. A further purpose is to provide a system thatwill be able to achieve the aforesaid objectives with relatively simpleand reliable means.

With a view to achieving the above and further purposes, the subject ofthe invention is a welding system of the type that has been specifiedabove, characterized moreover in that it comprises auxiliary guide meansthat connect directly at least one guide section of a magazine situatedupstream of the welding station with a guide section of a magazinesituated downstream of the welding station so as to enable transfer ofside frames directly from the magazine upstream to the magazinedownstream, and vice versa.

Thanks to the characteristic referred to above, during operation of thewelding station it is possible to guarantee that in any operatingcondition and in particular whatever the succession of the various typesof structure to be welded that advances through the welding station, thesystem will always be able to find each time the pair of side framesthat are necessary in the most advantageous position to enable it to bebrought into the working position before the corresponding type ofstructure to be welded arrives in the station, so as to guarantee thatno dead times are required for pre-arrangement of the frames that arenecessary in the welding position and so as to able, when a structure ofa type different from the one previously welded enters the weldingstation, to replace the side frames previously used with the new pair ofside frames that is necessary in a time not longer than the time ofalternation of the bodies to be welded in the station.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the annexed plateof drawings, in which:

FIG. 1 is a schematic view of a first example of embodiment of thesystem according to the invention; and

FIG. 2 is a perspective, once again schematic, view, of a variant of thesystem of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a welding system for motor-vehicle bodies that to amajor extent corresponds to the system known from the preceding Europeanpatent application No. EP-A-1 611 991, filed in the name of the presentapplicant.

The system comprises a welding station 1 set along a conveying line(represented only schematically by the arrow 2), used for carrying thebodies to be welded through the welding station 1. The station 1 is notillustrated in detail in so far as it is of a conception that is as awhole known, with the exception of some of its specific innovativeaspects, which will be described in what follows. The welding equipmentprovided in the station 1 can be constituted by robots of a known type(not illustrated in FIG. 1), the control unit of which contains a set ofdifferent operating programs, selected each time according to the typeof body to be welded.

Given that the conveying line 2 and the means for obtaining displacementof the bodies along it can be of any known type, said elements are notillustrated in the annexed plate of drawings in so far as they do notfall within the scope of the present invention. Their elimination fromthe drawings moreover renders the latter more immediatelyunderstandable. It is evident in any case that the way in which the bodyto be welded is formed in the welding station can be any whatsoever. Forexample, the body can be entirely pre-assembled in a provisional wayupstream of the welding station. Or else, the various sub-assembliesforming the body can be carried on the conveying line 2 to the weldingstation in an as yet non-assembled condition, assembly prior to weldingbeing performed in the station itself. Or yet again, the conveying line2 can carry only part of the body, for example the floor panel, to thewelding station, in which case the assembly of the complete body isperformed in the welding station, getting the remaining components ofthe body to arrive there. Again, the system of the invention is ofcourse usable also for welding individual sub-assemblies of body, oragain in theory for any other type of welded sheet-metal structure thatis to be produced in various types or models or versions. Whatever theway in which the body is assembled, it is necessary to clamp each partof the body in a precise position when the body undergoes the operationsof welding in the station 1. Said clamping is obtained by means of toolsfor positioning and clamping, carried by pairs of side frames that areoperatively interchangeable with one another, designated by 3 a, 3 b, 3c and 3 d in FIG. 1, which can run on longitudinal bottom rails orguides 4; where not strictly necessary for a detailed description of theoperation of the system according to the invention, the side frames 3 a,3 b, 3 c, and 3 d will in what follows be identified just by thereference number 3.

In the case exemplified, the guides 4 extend parallel to the line 2 forconveying the bodies and are fixed directly to the floor, with theexception of their respective intermediate portion, designated by 4 a,located in a position corresponding to the welding station 1. As willemerge clearly from what follows, the portions 4 a of the guides 4 canbe translated in a direction substantially perpendicular to thelongitudinal development of the guides themselves, for carrying the sideframes 3 of the pair in use into the welding station 1 in the respectiveclosed condition.

The pairs of frames 3 can be displaced along the guides 4 so as to carryinto a position corresponding to the welding station 1 a pair of sideframes corresponding to the type of body to be welded. When a body of atype different from the one on which the welding station has beenoperating immediately before reaches the station 1, the pair of sideframes that is located in the station can be rapidly replaced by slidingon the respective guides 4, as will emerge from what follows.

To increase the flexibility of the welding station and in particularincrease the number of different types of body on which the station isable to operate, in the case exemplified, two magazines of frames areprovided, situated, respectively, upstream and downstream of the weldingstation, with reference to the direction of advance along the line 2.Each of the two magazines of frames comprises a series of stations 6 aand 6 b, arranged at the two sides of the conveying line 2 and of theguides 4, where each station comprises a guide section 7 having a shapesimilar to the guides 4 and thus designed to support a correspondingside frame in a slidable way. In the case exemplified, the guidesections 7 extend substantially parallel to the guides 4.

In the example illustrated, both the magazine upstream and the magazinedownstream have two sections of magazine at the two sides of theconveying line 2, each comprising three different stations 6 a, 6 b,which corresponds to a maximum total number of six different types offrames 3 that are to operate on as many types of body. Of course, in anycase, the two magazines can be provided with any number of parkingstations, with the limits that will be illustrated in what follows.

The various frames 3 carry, in a way in itself known, respectivepositioning tools for clamping (not illustrated), designed to engage theside and top parts of the body, in such a way as to clamp it in aprecise position during execution of the operations of welding in thestation 1. The bottom part of the body is instead clamped by means offurther positioning tools for clamping, prearranged on the bottom partof the welding station 1. Each pair of side frames 3 is in particularprovided with positioning tools for clamping suited to the particularconfiguration of a respective type of body.

During use of the system, positioned each time on the guides 4 are afirst pair of side frames 3, in the working position, corresponding tothe type of body that is located each time in the welding station 1, anda second pair of frames 3, in a waiting position, corresponding to thetype of the body to be welded immediately after. When the latter bodyenters the welding station 1, the first frames 3 are carried into awaiting position and the second frames 3 into the working position bymeans of a simultaneous movement in the longitudinal direction along theguides 4.

Provided in a position corresponding to the two longitudinal ends of theguides 4 are respective translatable guide elements 8 a, 8 b having ashape similar to that of the guides 4. The translatable guide elements 8a, 8 b are equipped with respective motor-drive means 9 in order to beable to displace laterally, for example on respective pairs of rails 10a, 10 b, in a direction perpendicular to the longitudinal development ofthe guides 4, between a first position and a plurality of secondpositions. In the aforesaid first position, each translatable guideelement 8 a, 8 b is longitudinally aligned to a respective guide 4 so asto constitute a sort of prolongation thereof. By means of the aforesaidlateral displacement, each stretch 8 a, 8 b can be brought into aposition corresponding to a respective parking station 6 a, 6 b, i.e.,to a guide section 7.

Moving of the side frames 3 of the various pairs can be obtained invarious ways. In a first embodiment, which corresponds to what isillustrated in FIG. 1, moving of the side frames 3 of the various pairsis obtained by means of independent tractors, each of which is able toco-operate with different side frames 3 in order to pick them up from arespective station 6 a and 6 b and bring them into the operatingposition in a position corresponding to the station 1 and vice versa. Inthe case illustrated in FIG. 1, two pairs of tractors are provided,designated by 11 a and 11 b, which are selectively coupleable to thevarious side frames.

The welding system described above corresponds to what is illustrated inthe preceding European patent application No. EP-A-1 611 991, filed inthe name of the present applicant. The general operation of said systemis described in what follows. We shall assume that in the weldingstation 1 is a body of a first type referred to as type A, parts ofwhich are clamped in a precise position during the operations of weldingby positioning tools carried by the pair of side frames 3 a. The bodythat is located in the welding station 1 is to be followed by a body ofa second type, referred to as type B, where the positioning toolsprearranged for clamping the various parts of the body of type B duringexecution of welding are prearranged on the pair of the side frames 3 b.Likewise, we shall assume that the body of type B is followed by a bodyof a third type C, and this in turn by a body of a fourth type D, toeach of which is associated a respective type of side frames 3 c and 3d.

The replacement of one body in the welding station 1 with a body of adifferent type is accompanied by a corresponding replacement of thepairs of side frames to be used by the station itself along the guides4, in such a way as to bring one pair of side frames 3 into a waitingposition and the other pair of frames 3 into the operating position,corresponding to the welding station.

Once each pair of side frames has reached the operating position, it isdisplaceable between an open condition, to enable entrance into thewelding station 1 of the new body to be welded, and a closed position,in which the positioning tools of the side frames engage the side andtop parts of the body to clamp them in a precise position. As previouslymentioned, the aforesaid movement is obtained via translation of theportions 4 a of the guides 4. The clamping of the frames 3 in the closedcondition, with respect to the welding station, is obtained via means inthemselves known.

In FIG. 1, the bodies that advance along the line are not illustratedfor reasons of clarity. As long as bodies of type A and B advance alongthe line, they are welded each time after prior longitudinal sliding ofthe two pairs of side frames 3 a and 3 b in such a way that each timeone of said pairs reaches the operating position, and the other pair isbrought into a waiting position, respectively upstream and downstream ofthe welding station. In the situation illustrated in FIG. 1, located inthe operating position are the two side frames 3 a, which means that thebody that is located in the welding position is a body of type A. If,for example, after said body, a body of type C is to be welded, the twoside frames 3 b do not remain stationary in a waiting position, butinstead advance longitudinally along the guides 4 up to the positionillustrated in FIG. 1. In said condition, the guide sections 8 bdisplace transversely along the guides 10 b until they come intoalignment with respective guides 7 of two stations 6 b of the magazines.In this way, the side frames 3 b can be brought into an inoperativeposition in the magazine, after which the guide sections 8 b are alignedwith the sections 7, on which they await the two side frames 3 c. Thelatter can thus be taken on board the guide sections 8 b, which displaceonce again transversely until they are aligned with the guides 4. Inthis way, the two side frames 3 c can move into the waiting position,immediately downstream of the welding station, so that at the end ofwelding of the body of type A, they will be ready to translatelongitudinally along the guides 4 and move into the operating positionfor intervention on the body of type C, which is entering the weldingstation.

As has already been said, the structure and operation described aboveare known from the preceding patent application No. EP-A-1 611 991,filed in the name of the present applicant. The embodiment of thepresent invention illustrated in FIG. 1 differs from what is known fromthe preceding application in that, in the case illustrated, themagazines upstream and downstream provided in the welding system areconnected directly together by means of guide sections 70. In thespecific case illustrated, just two guide sections 70 are provided,which connect together two guide sections 7 on the two sides of thewelding station. It is not ruled out, however, that a greater number ofconnection sections 70 can be provided for connecting together more thantwo guide sections 7. As may be seen, the pre-arrangement of the guidesections 70 that connect directly together guide sections 7 belonging tomagazines arranged upstream and downstream of the welding stationenables conveying of a side frame from a magazine upstream of thestation directly to the magazine downstream, or vice versa, without theneed to pass the side frame through the longitudinal guides 4 arrangedat the two sides of the welding station. In other words, guide lines 70are provided that constitute a by-pass with respect to the longitudinalguides 4. Said solution enables the productivity of the system to beraised considerably and in particular guarantees once again thepossibility of positioning a pair of side frames rapidly in theoperating position, in whichever magazine station said side frames arearranged.

FIG. 1 refers to the case where, as in the preceding patent applicationfiled in the name of the present applicant moving of the side frames isobtained by means of independent tractors 11 a, 11 b, which are able tomove on the guides 4 and on the guide sections 7 and are able to engagewith the side frames.

FIG. 2 illustrates a similar welding station, in which each side frameis provided with an autonomous motor drive of its own. Also in the caseof FIG. 2, the robots R that carry the welding heads that are needed forcarrying out the operations of welding on the body that each time islocated in the welding station are not illustrated, and nor are thebodies that advance through the station illustrated.

FIG. 2 illustrates in particular a condition in which located along theguides 4 at the two sides of the line are two pairs of side frames andin which all the remaining types of side frames are located, positionedin the magazine downstream of the welding station. In the case of theexample illustrated in FIG. 2, there are once again provided a total offour pairs of side frames that are to operate on four different types ofbody. At the instant illustrated in FIG. 2, located in the weldingstation is a body of type A, engaged by the pair of frames 3 a, whilstthe pair of side frames 3 d are waiting. The magazine upstream iscompletely empty, and the side frames 3 b that were in the magazinedownstream, are in the course of transfer, via the guide sections 70,from the magazine downstream to the magazine upstream.

FIG. 2 differs then from FIG. 1 in that, in the system illustratedtherein, no frame 3 is carried by a self-driven trolley.

As may be seen, the principle that underlies the present invention isthat of creating a direct connection between the magazine upstream ofthe welding station and the magazine downstream of the welding station,so as to make it possible to carry side frames positioned in one of saidmagazines into the other magazine directly, and vice versa, withoutpassing through the guides 4 arranged at the two sides of the weldingstation.

Of course, without prejudice to the principle of the invention, thedetails of construction and the embodiments may vary widely with respectto what is described and illustrated herein, without thereby departingfrom the scope of the present invention.

In particular, the structure, conformation, and operation of the weldingstation can also be different from the ones illustrated above, and thesame also applies to the number, conformation, and arrangement of themagazines of side frames.

1. A system for welding structures constituted by elements of stampedsheet metal, such as motor-vehicle bodies or their sub-assemblies,designed to operate automatically on a plurality of different types ofstructures to be welded, of the type comprising: a welding station; aconveying line for carrying through the welding station the structuresto be welded or at least part thereof; a plurality of pairs of sideframes, which are provided with means for clamping the structures to bewelded and can be guided along the conveying line, the clamping meansprovided on the side frames of each pair being adapted to theconfiguration of a corresponding type of structure to be welded, whereinthe side frames are movable on guide means, provided at the side of theconveying line, to enable replacement, according to the type ofstructure to be welded, of the pair of side frames that is located atthe welding station, each side frame being displaceable between a firstposition, close to the welding station and at least one second position,remote with respect to the welding station, and wherein, when each pairof side frames is located in said first position close to the weldingstation, it is moreover displaceable between an open position and aclosed position, in which the respective side frames are operative forclamping parts of the structure to be welded in a welding configurationon the welding station, the system moreover comprising means for movingthe side frames for their displacement between the respective first andsecond positions, wherein there are provided one or more magazines offrames, each comprising one or more parking stations, both upstream anddownstream of the welding station, each station comprising a guidesection designed to support a side frame in a slidable way in its secondposition, said system being characterized in that auxiliary guide meansare provided that connect directly at least one guide section of amagazine upstream of the welding station with a guide section of amagazine downstream of the welding station, in such a way as to enabletransfer of pairs of side frames directly from the magazine upstream tothe magazine downstream, or vice versa, without passing them through thewelding station.
 2. The welding system according to claim 1, whereinsaid means for moving comprise a plurality of tractors, which areautonomous with respect to said side frames, each tractor beingselectively coupleable automatically to side frames of different pairs,in order to displace the latter.
 3. The welding system according toclaim 1, wherein said means for moving comprise motor means associatedto each side frame.